Plasmatron fuel converters or reformers (“plasmatrons”) reform hydrocarbons to generate a hydrogen rich gas which includes hydrogen and carbon monoxide through the use of plasma discharges. (See, for example, U.S. Pat. No. 6,322,757 to Cohn et al.; U.S. Pat. No. 5,887,554 to Cohn et al; U.S. Pat. No. 5,437,250 to Rabinovich et al; and U.S. Pat. No. 5,425,332 to Rabinovich et al.; and U.S. Pat. No. 6,793,899 to Bromberg et al, the teachings of all of which are incorporated herein by reference). Plasmatron fuel conversion using low current, high voltage discharges can provide significant advantages. (For a general treatise on plasma physics, see J. Reece Roth, Industrial Plasma Engineering, Vol. 1 and 2, Institute of Physics: Bristol, UK, 1995; for other examples of devices utilizing plasma technology, see U.S. Pat. Nos. 2,787,730; 3,018,409; 3,035,205; 3,423,562; 4,830,492; 4,963,792; and 4,967,118, the teachings of all of which are incorporated herein by reference).
Applications that require hydrogen onboard vehicles span a large range of flow rates. While at high engine loads, large hydrogen rich gas volumes are required (with corresponding high fuel flow rates through the plasmatron fuel reformer). Because of the infrequent operation of light duty vehicles in this regime, the operational characteristics of a fuel reformer at these high flow rates are less demanding than at lower flow rates. Thus the hydrogen conversion efficiency, defined as ratio of hydrogen flow in the reformate to hydrogen content in the fuel, and reformer power efficiency, defined as power content in the reformate to that in the fuel to the reformer, are not key requirements at these high flow rates. More importantly is the hydrogen conversion efficiency and the reformer power efficiency at low flow rates, where the flows are not large, but where the engine operates a large fraction of the time.
In addition to warm operation at low loads (which requires low fuel flow rates through the plasmatron), it is desirable to have low flow rates through the cold start period of engine operation. In order to minimize hydrocarbon emissions during a cold start period, operation in mainly reformate would be desired. However, because of the short duration of the cold start period, energy efficiency is not particularly important.
Generally, low current plasmatron systems known in the prior art operate at a fuel flow rate on the order of 1 g/s and produce on the order of 40 kW of reformate power. The dynamic range is about a factor of 3, which would be from 13 to 40 kW for a typical plasmatron. In plasmatrons having multiple air inputs (such as plasma stretching air, atomization air and wall protection air), the different requirements for these inputs may further limit the dynamic range. For example, for a fuel flow rate of ˜1 g/s and an Oxygen/Carbon (O/C) ratio of ˜1, the plasma air flow rate is preferably ˜90 liters per minute, the atomization air ˜57 liters/min, and the wall protection air ˜115 liters/min. For a fuel flow rate of ˜0.1 g/s and O/C˜1, the plasma air flow rate is preferably ˜15 liters/min, the atomization air ˜10 liters/min, and the wall protection air flow rate is at zero. At these parameters, fuel atomization and initiation of reforming in the plasmatron can be degraded and soot production increased. By providing a plasmatron fuel reformer system having a wide dynamic range, improvements are possible in fuel injection (at both high and low range), air injection (at both high and low range) and power supply requirements, which ideally may be varied with air/fuel flow rate and conditions.
Accordingly, there is a need for a plasmatron reformer system capable of wide dynamic range operation which is of particular importance for use with vehicular gasoline engines which operate over a wide fuel flow range.